id_dspi
Purpose
Direct structural system parameter identification.
Syntax
[a,b,c,d] = id_dspi(y,u,w,IDopt,np)
Description
The direct structural system parameter identification algorithm
[49] considered here, uses the displacement frequency responses
y(s) at the different sensors corresponding to the frequency domain
input forces u(s) (both given in the xf format). For example
in a SIMO system with a white noise input, the input is a column of
ones u=ones(size(w)) and the output is equal to the transfer
functions y=xf. The results of this identification algorithm
are given as a state-space model of the form
|
{ |
|
} = [ |
|
]
{ |
|
} + [ |
|
] {u}
and
{y} = [ |
|
] { |
|
}
|
where the pseudo-stiffness KT and damping CT
matrices are of dimensions np by np (number of normal
modes). The algorithm, only works for cases where np is smaller
than the number of sensors (IDopt.ns).
For SIMO tests, normal mode shapes can then be obtained using [mode,freq] = eig(-a(np+[1:np],1:np)) where it must be noted that the
modes are not mass normalized as assumed in the rest of the
Toolbox and thus cannot be used directly for predictions (with
nor2xf for example). Proper solutions to this and other difficulties
linked to the use of this algorithm (which is provided here mostly for
reference) are not addressed, as the main methodology of this
Toolbox (id_rc, id_rm, and id_nor) was found to be more accurate.
For MIMO tests, id_dspi calls id_rm to build a MIMO model.
The identification is performed using data within IDopt.SelectedRange.
y is supposed to be a displacement. If IDopt.DataType gives y
as a velocity or acceleration, the response is integrated to displacement as a first step.
See also
idopt, id_rc, id_rm, psi2nor, res2nor
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